Internal field 59Co NMR study of cobalt-iron nanoparticles

The catalytic growth of carbon nanotubes by catalytic carbon vapor deposition (CCVD) can be performed on variety of Co, Fe, and Ni catalysts. It is typically a three-step process where an induction period is followed by a steady-state growth and finally an asymptotic approach to the maximal tube length. However, the transition between induction and growth is not yet fully understood.

In the appropriate range of temperature and size, iron and cobalt metal nanoparticles are ferromagnetic opening the unique possibility to perform 59Co or 57Fe NMR in the internal field of the catalysts particles. By mobilizing the potential of the method, we shed new light on what happens during the first tens of seconds in the reactor. During activation, the pure Co metal content dropped and an increase of the ordering of the cobalt-iron alloy in the catalyst was evidenced thus revealing a multistage activation mechanism for the reaction. We propose this ordering process during the induction period to be an intermediate step between the strong ferromagnetic Co rich alloy and the weak ferromagnetic Fe rich one and that it favors the onset of MWCNTs growth.

To know more : Internal field 59Co NMR study of cobalt-iron nanoparticles during the activation of CoFe2/CaO catalyst for carbon nanotube synthesis.